Tunnel kiln

ABSTRACT

A tunnel kiln in which the roof of the heating zone of the kiln is made in the form of a double arch arrangement providing a plenum chamber for preheating combustion air for the burner means. Air is supplied to the air preheat chamber from the cooling zone of the kiln and is delivered from the air preheat chamber to the burner means to provide combustion air therefor.

United States Patent 11 1 Remmey et al.

1451 .Huly 10,1973

[ TUNNEL KILN [75] Inventors: George Bickley Remmey,

Huntingdon Valley, Pa.; Charles A. McFadden, Medford, NJ.

[73} Assignee: Bickley Furnace Incorporated, Bucks County, Pa.

{22] Filed: Nov. 29, 1971 {21] Appl. No.: 202,893

[52] U.S. Cl. 432/137 [51] Int. Cl. F27b 9/00 [58] Field of Search 263/28; 25/142 G,

25/142 H, 142 HA, 142 K; 432/137, 241

[56] References Cited UNITED STATES PATENTS 2,325,572 7/1943 Robson et a]. 25/142 K Booth 263/28 X Cook et al. 263/28 Primary Examiner-John J. Camby Att0rney-Frank A. Follmer [5 7] ABSTRACT A tunnel kiln in which the roof of the heating zone of the kiln is made in the form of a double arch arrangement providing a plenum chamber for preheating combustion air for the burner means. Air is supplied to the air preheat chamber from the cooling zone of the kiln and is delivered from the air preheat chamber to the burner means to provide combustion air therefor.

16 (Claims, 4 Drawing Figures Patehted July m, 1973 2 Sheets-Shee t l NOT Patented July 10, 1973 2 Sheets-Shee t P FIG. 2.

FIG. 3.

FIG. 4.

TUNNEL KILN BACKGROUND OF THE INVENTION The invention relates generally to tunnel kilns of the type shown in U. S. Pat. No. 3,464,682, and more particularly to tunnel kilns having a firing zone in which the heating gases achieve very high temperatures of the order of up to about 3,500 F. It will be evident that the invention is applicable to other continuous heat treating furnaces, such as for example, roller hearth furnaces, conveyor belt furnaces and the like for the processing of metals, glass, etc.

Prior art tunnel kilns have not proved entirely satisfactory in many applications since these kilns cannot achieve accurate fuel/air ratioing by the burners, require the use of expensive thermally shock sensitive refractories in the roof portion of the kiln in the firing zone, and involve reduced fuel efficiency. The failure to provide accurate fuel/air ratioing of the burners results in a condition in which the amount of oxygen in the gases in the ware treating chamber of the kiln cannot be maintained at desired levels along the length of the firing section. Many types of ware treated in kilns are adversely affected by an atmosphere having a high percentage of oxygen.

SUMMARY OF THE INVENTION It is the general object of this invention to provide a high temperature tunnel kiln which has improved fuel efficiency and which is constructed and arranged to supply a controllable quantity of preheated air to each of selected burner means of the kiln in order to meet the requirements of accurate fuel/air ratioing by each of the burner means whereby the oxygen levels along this region of the kiln chamber are maintained at desired amounts. In addition, the kiln in accordance with the invention utilizes the preheated air to cool the roof portion of the kiln in the firing zone wherefore the life of the refractory at this location is enhanced, less expensive refractories can be used, and more economical wider kilns can be built.

Briefly stated, the general object of the invention is achieved by the provision of a tunnel kiln comprising a wall means defining a horizontally extending kiln chamber, this wall means including along a zone of the kiln a pair of vertical side walls and a roof extending across the top of the kiln between these side walls, the roof including spaced inner and outer portions defining an air preheat chamber providing a plenum extending along the kiln in the roof of the zone. There are provided means for introducing high velocity heating fluid streams into the kiln chamber at a plurality of locations spaced along the zone, and means for supplying air to the air preheat chamber whereby the air becomes heated by reason of its heat transfer relationship with the heating gases within the kiln chamber through the inner wall of the roof. There are means connected between the air preheat chamber and the fluid introducing means for delivering the heated air from the plenum to the fluid introducing means.

Other features of the invention relate to the control of the fluid introducing means and the preheated air supplied thereto and the construction and arrangement thereof.

FIG. 3 is a side elevation of adjacent sections of the tunnel kiln in accordance with the invention;

FIG. 2 is a sectional view taken on line 22 of FIG.

FIGS. 3 and 4 are fragmentary views showing details of the gas introducing means.

DESCRIPTION OF THE PREFERRED EMBODIMENT The tunnel kiln in accordance with the invention comprises a horizontally extending structure defining a longitudinal tunnel kiln chamber 10 defined by a lining of suitable refractory material. The kiln structure is made up of a plurality of sections as is best shown in FIG. 1. Each of these sections is made up of a roof supported on vertical side walls, these sections being indicated generally at l2, l4, 16, 18 and 20. With the exception of section 16 wherein a special roof construction is provided in accordance with the invention, the roofs of the other kiln sections may take various forms at various locations along the kiln and may be of a suspended arch construction or a sprung arch construction as is well known in the art. The type and size of refractory materials at various locations along the kiln are chosen in accordance with the particular temperature condition associated therewith as is also well known in the art. The retractory walls are supported in steel plate casings with welded structural steel reinforcements or may be supported in building brick casings in accordance with well known practices. The structural aspects of the kiln will be apparent to those skilled in the art.

The bottom of the kiln is formed by refractory floors supported on the usual kiln cars, such as shown by the car 22 in FIG. 2, which cars ride on conventional rails 24. The kiln cars extend end-toend along the length of the tunnel kiln as is conventional in the art.

It will be noted that the kiln cars 22 are moved through the kiln in the direction from left to right in FIG. 1, the section 12 being at the entrance end of the kiln and the section 20 being at the exit end of the kiln. The kiln cars are moved through the kiln by way of a hydraulic pusher mechanism such as that described more fully in said US. Pat. No. 3,464,682.

At the inlet of the kiln there is provided a conventional vestibule 30 which includes a pair of vertically sliding doors 32 and 34 arranged to move vertically to close the inlet end of the kiln when desired. The purpose of the vestibule arrangement is to prevent air from being drawn into the kiln through the inlet end when the kiln cars are introduced into the kiln.

Section 12 at the inlet of the kiln is provided with a conventional exhaust system 38 for removal of the products of combustion.

At section 20 at the exit end of the kiln which is actually a cooling zone, there is provided an exhaust system 40 for the cooling gas. There is also shown a cooling air jet fan 42 which supplies cooling air to the cooling air jets 44 and 46 on the near and far side of the kiln in the section 20 which is the cooling zone of the kiln. The various fan operated systems 38, 40 and 42 and the cooling air jets 44 are described more fully in said U.S. Pat. No. 3,464,682 and form no part of the present invention, wherefore further description thereof is deemed unnecessary.

The kiln cars 22 are provided with a horizontal platform 26 for supporting the ware indicated at W. As is described more fully in said U.S. Pat. No. 3,464,682, the ware is arranged on platform 26 in order to provide fire lanes extending transversely across the kiln chamber.

There are provided along the length of the kiln a plu rality of individual firing sections, these sections being spaced equally and longitudinally along the kiln and have provided thereat means for introducing either heating or cooling gases into the kiln in the form of high velocity gas streams. This is described more fully in said U.S. Pat. No. 3,464,682.

Heating gases are introduced into the kiln in the zones indicated at C, E, F, G, H, and J. The kiln is designed so that the temperature of the ware is raised gradually in zones A and B by countercurrent flow of the heating gases by the exhaust fan action to the high temperature condition which is maintained throughout zones C, D, E, F, G, H and J. The temperature will then drop off in zone K and continue to drop off in the rest of the kiln, section being devoted to the cooling of the ware by the introduction of cooling air. The manner in which this can be achieved by controlling the individual gas introducing means is described more fully in said U.S. Pat. No. 3,464,682.

In the high temperature section of the kiln there are provided fluid introducing means on the near side of the kiln indicated at 50 and fluid introducing means at the far side of the kiln are indicated at 52. In this manner, the means50 and 52 are arranged so that in each fire lane heating fluids are introduced into the kiln in a transverse direction opposite to that of an adjacent firing lane. Y

The fluid introducing means provided in the high temperature section 16 of the kiln is shown in detail in FIGS. 3 and 4. Each of the fluid introducing means 50 and 52 shown is a gas type and is provided with burner assemblies including a high velocity jet burner 60 mounted on the associated vertical wall of the section 16 and having its discharge end directing a high velocity gas stream through a chamber 62 and through a passage 64 formed in a block 66, as is best shown in FIG. 3. It is noted that the burner 60 is supported on a block 68 and a bracket support 70 so as to direct its fuel containing stream in the manner described transversely into the kiln chamber 10. The fuel, in the form of an air/gas mixture is supplied to the jet burner 60 through a pipe 72 which has its upstream end connected to a mixing tee 74. Air is supplied to the mixing tee 74 through an air supply line 76 which is regulated by an air flow control valve 78 and a metering orifice 79. The fuel gas is supplied to the mixing tee 74 from the gas supply line 80 through a line indicated generally at 82 comprising a gas flow control valve 84 and a metering orifice 86.

It will thus be apparent that the gas/air mixture supplied to the jet burner 60 may be varied in the proportions desired for a particular application. In fact, in some applications, it may be appropriate to supply raw fuel to the jet burner. Moreover, the gas supply is maintained at a high pressure so that a high velocity fuel containing gas stream is discharged from the nozzle of the jet burner 60.

Also, while the present invention is described as employing gas/air burners, it is to be noted that it may also employ fuel oil burners. The oil burners would require means for atomizing the fuel oil prior to its mixture with the combustion air. Moreover, the oil burners may use oil or an oil/air mixture as the fuel supply. Accordingly, the generic term fluid introducing means is used herein to apply to oil or gas means.

In accordance with the invention, in the embodiment thereof shown there is provided means for supplying preheated air to the fluid introducing means 50 and 52 for the high temperature kiln section 16. To this end, the roof 58 of the high temperature kiln section 16 is constructed in a double arch configuration comprising an inner wall portion 92 adjacent the'kiln chamber 10 and an outer wall portion 94 spaced above wall portion 92 to define an arcuate preheat chamber 96. The chamber 96 extends across the kiln in an arcuate shape between the walls 54 and 56, as is shown in FIG. 2, and extends longitudinally along the length of the high temperature section 16, as is shown in FIG. 1. The chamber is constructed of a size so as to form a plenum for the distribution of preheated air to the burner means as described hereafter.

There is provided means for supplying warmed air to the preheat plenum 96, such means comprising an air supply fan 100, the delivery end of which is connected through a conduit 102 to the plenum 96, as is shown in FIG. 1. The inlet of the fan is connected to a conduit 104 which is connected through an air intake line 106 to the kiln chamber 10 at a location within cooling section 20 of the kiln wherein the air is in a warmed condition. The flow through the conduit 104 is controlled by an air control valve 108. In this manner the fan 100 operates to draw warmed air from the cooling zone of the kiln chamber 10 through intake line 106, conduit 104 and deliver this air through conduit 102 into the double arched preheat plenum 96. It will be apparent that the air delivered to the plenum 96 will be further heated above its entry temperature, as it moves through the plenum, by reason of the heat exchange relationship between this air and the very high temperature gases in the kiln chamber 10 by way of the heat conduction through the arched inner wall portion 92.

Means are provided for delivering the heated air from the air preheat chamber 96 to the fluid introducing means 50 and 52. To this end, there is provided a plurality of vertically extending passages 110 and 112 in the walls 54 and 56, respectively, the passages 110 and 1 12 providing communication between the plenum 96 and the chambers 62 associated with each of the fluid introducing means 50 and 52. This communication is best shown in FIG. 3. A hot air flow metering valve in the form of a plate of refractory material 114 is mounted in each block 68 for slideable movement to control each of the passages 110 and 112 at its juncture with the respective chambers 62. In this manner the flow from passages 110 and 112 to chambers 62 can be regulated by varying the size of the interconnecting passage therebetween.

There is provided a preheated air pressure control means which maintains a predetermined differential pressure between the air in chamber 96 and the gases in the kiln chamber 10. For example, a pressure differential of 0.20 inches of water column would insure the maintenance of a positive pressure condition which is preferred (i.e., the pressure in the air preheat chamber 96 is at all times greater than the pressure in heating zone of the chamber 10). On the other hand, the pressure in chamber 96 can be maintained equal to or less than the pressure in the heating zone of chamber 10. This means comprises a control 120 for the fan 100, which comprises a pressure controller 122 and a pressure transducer 124. The pressure transducer 124 is connected through lines 125 and 127, respectively, to a pressure tap 126 which senses the pressure in chamber 96 and a pressure tap 128 which senses the pressure in the kiln chamber 10. The control means comprises conventional elements and operates to sense the differential pressure in the chambers and 96 and actuate the transducer 124 which in turn actuates the pressure controller 122 to control flow control valve 108 of fan 1G0. This type of pressure control is conventional.

in the operation of the tunnel kiln in accordance with the invention, warmed air is delivered to the air preheat plenum 96 by the fan 100 which draws warmed air through the intake line 106 and line 104 from a cooling zone of the kiln and delivers the warmed air through the line 102 to the plenum 96. This air delivery is controlled by the control means 120 which controls the flow control valve 108 of fan 100 so as to maintain a positive pressure differential between the plenum 96 and the kiln chamber 10 in the high temperature section in. The air passes through the plenum 96 to the various vertical passages 110 and 112 at the controlled pressure and through these passages to the fluid introducing means 50 and 52, respectively spaced along the high temperature section 16. The air is further heated as it moves through the preheat plenum 96 since it passes over the outer face of the wall portion 92, this outer face being at an elevated temperature since it is heated by conduction through wall 92 the inner or hot face of which is heated by the high temperature gases in the kiln chamber 10. The fluid introducing means 50 and 52 are set to deliver high velocity heating fluid streams into the kiln chamber 10 in a direction transversely thereacross. The fluid streams directed from the jet burners 60 induct air from the vertical passages 110 and 112 and since this secondary air is preheated, high flame temperatures are produced and a very efficient fuel consumption is achieved by the burner assemblies. It will be noted that what occurs is that the heat which is transferred through the inner wall portion 92 of the double arch construction, and which is normaliy lost to the surrounding atmosphere in conventional kiln designs, is fully recovered by virtue of its being picked up by the air passing through the plenum, which air is returned to the kiln chamber through the combustion reaction within the burner means.

By reason of the above-described construction and arrangement of the elements of the tunnel kiln in accordance with the invention, it will be evident that the air supplied to each of the fluid introducing means can be set to provide a controllable quantity of preheated air to each of the burner means in order to meet the requirements of accurate fuel/air ratioing by each of the burner means whereby the oxygen levels along this region of the kiln chamber can be maintained at desired amounts. Moreover, a very efficient fuel consumption is achieved as described above. Furthermore, the movement of the air through the plenum 96 serves to cool down the outer face of the inner wall portion 92 of the double arch construction to a temperature lower than the temperature that would be achieved with a conventional solid roof construction. This permits the use of refractory materials which are less expensive, which are more readily available, and which are substantially less sensitive to thermal shock. Moreover, by reason of the lower temperature conditions existing in the roof of the kiln, the life of the refractory at this location is enhanced and wider kilns can be built. It will be apparent that wider kilns will achieve greater production output within a much shorter length thereby resulting in substantial economies in the cost of constructing the kiln and in the cost of constructing the factory building required to house the kiln. Additionally, wider kilns have substantially greater fuel efficiency because there is less total wall area through which heat can be lost.

it will be apparent that various changes may be made in the construction and arrangement of the elements of the invention described above without departing from the scope of the invention.

We claim:

ll. A tunnel kiln or the like comprising wall means defining a horizontally extending kiln chamber, said wall means including along a zone of the kiln a pair of vertical side walls and a roof extending across the top of the zone of the kiln between said side walls, said roof including an inner wall portion adjacent the kiln chamber and an outer wall portion spaced above said inner wall. portion to define an air preheat chamber providing a plenum extending along said zone in said roof, means for introducing high velocity heating fluid streams into said kiln chamber at a plurality of spaced locations along said zone, means for supplying air to said preheat chamber, the air moving through said preheat chamber being heated by reason of its heat exchange relationship with said inner wall portion of said roof, and means connected between said preheat chamber and said fluid introducing means for delivering preheated air from said preheat chamber to said fluid introducing means.

2. A tunnel kiln according to claim 1 wherein said inner and outer wall portions are arranged in a double arch configuration defining an arcuate plenum.

3. A tunnel kiln according to claim ll wherein said fluid introducing means include burner assemblies arranged in said side walls to direct heating streams into the kiln chamber in a transverse direction.

4. A tunnel kiln according to claim 3 wherein said burner assemblies include jet burners arranged to direct the high velocity streams into the kiln chamber.

5. A tunnel kiln according to claim 4 including means for supplying said preheated air to said fluid introducing means at a location downstream of the discharge end of said jet burners.

6. A tunnel kiln according to claim 3 wherein said preheat chamber extends across the width of said zone of the kiln and wherein said means for delivering air from said preheat chamber to said fluid introducing means includes passage means formed in said side walls extending from said preheat chamber to each of said fluid introducing means.

7. A tunnel kiln according to claim 6 including valve means in each of said passage means for regulating the flow of preheated air through said passage means.

8. A tunnel kiln according to claim 7 wherein said means for supplying air to said preheat chamber includes fan means, conduit means connecting the inlet end of said fan means to an air containing cooling zone of said kiln chamber, and conduit means connecting the delivery end of said fan means to said preheat chamber, said fan means being constructed and arranged to draw air from the kiln chamber and deliver it to the preheat chamber.

9. A tunnel kiln according to claim 8 including means for controlling said fan to operate the same to maintain a set pressure differential between the pressure in said preheat chamber and the pressure in said zone of the kiln chamber.

10. A tunnel kiln according to claim 9 wherein said control means includes a pressure tap for sensing the pressure in said preheat chamber and a pressure tap for sensing the pressure in the kiln chamber along said zone.

11. A tunnel kiln according to claim 1 wherein said means for supplying air to said preheat chamber includes fan means, conduit means connecting the inlet end of said fan means to an air containing cooling zone of said kiln chamber, and conduit means connecting the delivery end of said fan means to said preheat chamber, said fan means being constructed and arranged to draw air from the kiln chamber and deliver it to the preheat chamber.

12. A tunnel kiln according to claim 11 including means for controlling said fan to operate the: same to maintain the pressure in said preheat chamber at a desired value relative to the pressure in the kiln chamber along said heating zone.

13. A tunnel kiln according to claim 3 wherein said fluid introducing means include burner assemblies ineluding jet burners arranged to direct a fuel containing high velocity gas stream into the kiln chamber, and ineluding means for supplying said preheated air to said flud introducing means at a location downstream of the discharge end of said jet burners wherefore the air is inducted into said high velocity gas stream.

14. A tunnel kiln according to claim 13 wherein said means for supplying air to said preheat chamber includes fan means, conduit means connecting the inlet end of said fan means to an air containing cooling zone of said kiln chamber, and conduit means connecting the delivery end of said fan means to said preheat chamber, said fan means being constructed and arranged to draw air from the kiln chamber and deliver it to the preheat chamber.

15. A tunnel kiln according to claim 14 including means for controlling said fan to operate the same to maintain the pressure in said preheat chamber greater than the pressure in the kiln chamber along said heating zone so that the preheated air supplied to each of said fluid introducing means is under a controlled pressure for accurate fuel/air ratioing.

16. A tunnel kiln according to claim 1 wherein said means for supplying air to said preheat chamber includes fan means, conduit means connecting the inlet end of said fan means to an air containing cooling zone of said kiln chamber, and conduit means connecting the delivery end of said fan means to said preheat chamber, said fan means being constructed and arranged to draw air from the kiln chamber and deliver it to the preheat chamber. 

1. A tunnel kiln or the like comprising wall means defining a horizontally extending kiln chamber, said wall means including along a zone of the kiln a pair of vertical side walls and a roof extending across the top of the zone of the kiln between said side walls, said roof including an inner wall portion adjacent the kiln chamber and an outer wall portion spaced above said inner wall portion to define an air preheat chamber providing a plenum extending along said zone in said roof, means for introducing high velocity heating fluid streams into said kiln chamber at a plurality of spaced locations along said zone, means for supplying air to said preheat chamber, the air moving through said preheat chamber being heated by reason of its heat exchange relationship with said inner wall portion of said roof, and means connected between said preheat chamber and said fluid introducing means for delivering preheated air from said preheat chamber to said fluid introducing means.
 2. A tunnel kiln according to claim 1 wherein said inner and outer wall portions are arranged in a double arch configuration defining an arcuate plenum.
 3. A tunnel kiln according to claim 1 wherein said fluid introducing means include burner assemblies arranged in said side walls to direct heating streams into the kiln chamber in a transverse direction.
 4. A tunnel kiln according to claim 3 wherein said burner assemblies include jet burners arranged to direct the high velocity streams into the kiln chamber.
 5. A tunnel kiln according to claim 4 including means for supplying said preheated air to said fluid introducing means at a location downstream of the discharge end of said jet burners.
 6. A tunnel kiln according to claim 3 wherein said preheat chamber extends across the width of said zone of the kiln and wherein said means for delivering air from said preheat chamber to said fluid introducing means includes passage means formed in said side walls extending from said preheat chamber to each of said fluid introducing means.
 7. A tunnel kiln according to claim 6 including valve means in each of said passage means for regulating the flow of preheated air through said passage means.
 8. A tunnel kiln according to claim 7 wherein said means for supplying air to said preheat chamber includes fan means, conduit means connecting the inlet end of said fan means to an air containing cooling zone of said kiln chamber, and conduit means connecting the delivery end of said fan means to said preheat chamber, said fan means being constructed and arranged to draw air from the kiln chamber and deliver it to the preheat chamber.
 9. A tunnel kiln according to claim 8 including means for controlling said fan to operate the same to maintain a set pressure differential between the pressure in said preheat chamber and the pressure in said zone of the kiln chamber.
 10. A tunnel kiln according to claim 9 wherein said control means includes a pressure tap for sensing the pressure in said preheat chamber and a pressure tap for sensing the pressure in the kiln chamber along said zone.
 11. A tunnel kiln according to claim 1 wherein said means for supplying air to said preheat chamber includes fan means, conduit means connecting the inlet end of said fan means to an air containing cooling zone of said kiln chamber, and conduit means connecting the delivery end of said fan means to said preheat chamber, said fan means being constructed and arranged to draw air from the kiln chamber and deliver it to the preheat chamber.
 12. A tunnel kiln according to claim 11 including means for controlling said fan to operate the same to maintain the pressure in said preheat chamber at a desired value relative to the pressure in the kiln chamber along said heating zone.
 13. A tunnel kiln according to claim 3 wherein said fluid introducing means include burner assemblies including jet burners arranged to direct a fuel containing high velocity gas stream into the kiln chamber, and including means for supplying said preheated air to said fluid introducing means at a location downstream of the discharge end of said jet burners wherefore the air is inducted into said high velocity gas stream.
 14. A tunnel kiln according to claim 13 wherein said means for supplying air to said preheat chamber includes fan means, conduit means connecting the inlet end of said fan means to an air containing cooling zone of said kiln chamber, and conduit means connecting the delivery end of said fan means to said preheat chamber, said fan means being constructed and arranged to draw air from the kiln chamber and deliver it to the preheat chamber.
 15. A tunnel kiln according to claim 14 including means for controlling said fan to operate the same to maintain the pressure in said preheat chamber greater than the pressure in the kiln chamber along said heating zone so that the preheated air supplied to each of said fluid introducing means is under a controlled pressure for accurate fuel/air ratioing.
 16. A tunnel kiln according to claim 1 wherein said means for supplying air to said preheat chamber includes fan means, conduit means connecting the inlet end of said fan means to an air containing cooling zone of said kiLn chamber, and conduit means connecting the delivery end of said fan means to said preheat chamber, said fan means being constructed and arranged to draw air from the kiln chamber and deliver it to the preheat chamber. 